I'm not at home to try it, BUT you might be able to use Photoshop (and if you don't own PS, then I suggest gimp)
http://www.gimp.org/A lot less intuitive or at least hard to translate if you've used PS before and then try to go right to gimp. Anyway, you can pick a color to become a transparent. I'm not sure how well that will work because if there is black in the book of the same value, it also becomes transparent. You may be able to fill the exterior black with another color, and then turn that color transparent. If you're interested in trying, I can see if I can dig up the tutorial I watched some time ago to do this with gimp.